%% Copyright (c) 2016-2019, Loïc Hoguin <essen@ninenines.eu>
%%
%% Permission to use, copy, modify, and/or distribute this software for any
%% purpose with or without fee is hereby granted, provided that the above
%% copyright notice and this permission notice appear in all copies.
%%
%% THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
%% WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
%% MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
%% ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
%% WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
%% ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
%% OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

-module(gun_http2).

-export([check_options/1]).
-export([name/0]).
-export([opts_name/0]).
-export([has_keepalive/0]).
-export([default_keepalive/0]).
-export([init/4]).
-export([switch_transport/3]).
-export([handle/4]).
-export([handle_continue/5]).
-export([update_flow/4]).
-export([closing/4]).
-export([close/4]).
-export([keepalive/3]).
-export([headers/11]).
-export([request/12]).
-export([data/7]).
-export([connect/7]).
-export([cancel/5]).
-export([timeout/3]).
-export([stream_info/2]).
-export([down/1]).
%-export([ws_upgrade/10]).

-record(stream, {
	id = undefined :: cow_http2:streamid(),

	%% Reference used by the user of Gun to refer to this stream.
	%% This may be only a part of a stream_ref() for tunneled streams.
	ref :: reference(),

	%% Process to send messages to.
	reply_to :: pid(),

	%% Flow control.
	flow :: integer() | infinity,

	%% Request target URI.
	authority :: iodata(),
	path :: iodata(),

	%% Content handlers state.
	handler_state :: undefined | gun_content_handler:state(),

	%% CONNECT tunnel.
	tunnel :: {module(), any(), gun:tunnel_info()}
		| {setup, gun:connect_destination(), gun:tunnel_info()}
		| {tls_handshake, gun:connect_destination(), gun:tunnel_info()}
		| undefined
}).

-record(http2_state, {
	socket :: inet:socket() | ssl:sslsocket(),
	transport :: module(),
	opts = #{} :: gun:http2_opts(),
	content_handlers :: gun_content_handler:opt(),
	buffer = <<>> :: binary(),

	%% Base stream ref, defined when the protocol runs
	%% inside an HTTP/2 CONNECT stream.
	base_stream_ref = undefined :: undefined | gun:stream_ref(),

	%% Current status of the connection. We use this to ensure we are
	%% not sending the GOAWAY frame more than once, and to validate
	%% the server connection preface.
	status = preface :: preface | connected | goaway | closing,

	%% HTTP/2 state machine.
	http2_machine :: cow_http2_machine:http2_machine(),

	%% Currently active HTTP/2 streams. Streams may be initiated either
	%% by the client or by the server through PUSH_PROMISE frames.
	%%
	%% Streams can be found by ID or by Ref. The most common should be
	%% the idea, that's why the main map has the ID as key. Then we also
	%% have a Ref->ID index for faster lookup when we only have the Ref.
	streams = #{} :: #{cow_http2:streamid() => #stream{}},
	stream_refs = #{} :: #{reference() => cow_http2:streamid()},

	%% We must queue commands when parsing the incoming data.
	commands_queue = [] :: [{set_cookie, iodata(), iodata(), cow_http:status(), cow_http:headers()}]
}).

check_options(Opts) ->
	do_check_options(maps:to_list(Opts)).

%% @todo Accept http_opts, http2_opts, and so on.
do_check_options([]) ->
	ok;
do_check_options([{closing_timeout, infinity}|Opts]) ->
	do_check_options(Opts);
do_check_options([{closing_timeout, T}|Opts]) when is_integer(T), T > 0 ->
	do_check_options(Opts);
do_check_options([Opt={content_handlers, Handlers}|Opts]) ->
	case gun_content_handler:check_option(Handlers) of
		ok -> do_check_options(Opts);
		error -> {error, {options, {http2, Opt}}}
	end;
do_check_options([{flow, InitialFlow}|Opts]) when is_integer(InitialFlow), InitialFlow > 0 ->
	do_check_options(Opts);
do_check_options([{keepalive, infinity}|Opts]) ->
	do_check_options(Opts);
do_check_options([{keepalive, K}|Opts]) when is_integer(K), K > 0 ->
	do_check_options(Opts);
do_check_options([Opt={Name, _}|Opts]) ->
	%% We blindly accept all cow_http2_machine options.
	HTTP2MachineOpts = [
		connection_window_margin_size,
		connection_window_update_threshold,
		enable_connect_protocol,
		initial_connection_window_size,
		initial_stream_window_size,
		max_connection_window_size,
		max_concurrent_streams,
		max_decode_table_size,
		max_encode_table_size,
		max_frame_size_received,
		max_frame_size_sent,
		max_stream_window_size,
		preface_timeout,
		settings_timeout,
		stream_window_margin_size,
		stream_window_update_threshold
	],
	case lists:member(Name, HTTP2MachineOpts) of
		true -> do_check_options(Opts);
		false -> {error, {options, {http2, Opt}}}
	end.

name() -> http2.
opts_name() -> http2_opts.
has_keepalive() -> true.
default_keepalive() -> 5000.

init(_ReplyTo, Socket, Transport, Opts0) ->
	%% We have different defaults than the protocol in order
	%% to optimize for performance when receiving responses.
	Opts = Opts0#{
		initial_connection_window_size => maps:get(initial_connection_window_size, Opts0, 8000000),
		initial_stream_window_size => maps:get(initial_stream_window_size, Opts0, 8000000)
	},
	{ok, Preface, HTTP2Machine} = cow_http2_machine:init(client, Opts),
	Handlers = maps:get(content_handlers, Opts, [gun_data_h]),
	BaseStreamRef = maps:get(stream_ref, Opts, undefined),
	%% @todo Better validate the preface being received.
	State = #http2_state{socket=Socket, transport=Transport, opts=Opts,
		base_stream_ref=BaseStreamRef, content_handlers=Handlers,
		http2_machine=HTTP2Machine},
	Transport:send(Socket, Preface),
	{connected, State}.

switch_transport(Transport, Socket, State) ->
	State#http2_state{socket=Socket, transport=Transport}.

%% This function is called before returning from handle/4.
handle_ret(CommandOrCommands, #http2_state{commands_queue=[]}) ->
	empty_commands_queue(CommandOrCommands);
handle_ret(Commands, #http2_state{commands_queue=Queue}) when is_list(Commands) ->
	lists:reverse(Queue, empty_commands_queue(Commands));
handle_ret(Command, #http2_state{commands_queue=Queue}) ->
	lists:reverse([empty_commands_queue(Command)|Queue]).

empty_commands_queue([{state, State}|Tail]) -> [{state, State#http2_state{commands_queue=[]}}|Tail];
empty_commands_queue([Command|Tail]) -> [Command|empty_commands_queue(Tail)];
empty_commands_queue([]) -> [];
empty_commands_queue({state, State}) -> {state, State#http2_state{commands_queue=[]}};
empty_commands_queue(Command) -> Command.

handle(Data, State=#http2_state{buffer=Buffer}, EvHandler, EvHandlerState) ->
	parse(<< Buffer/binary, Data/binary >>, State#http2_state{buffer= <<>>},
		EvHandler, EvHandlerState).

parse(Data, State0=#http2_state{status=preface, http2_machine=HTTP2Machine},
		EvHandler, EvHandlerState0) ->
	MaxFrameSize = cow_http2_machine:get_local_setting(max_frame_size, HTTP2Machine),
	case cow_http2:parse(Data, MaxFrameSize) of
		{ok, Frame, Rest} when element(1, Frame) =:= settings ->
			case frame(State0#http2_state{status=connected}, Frame, EvHandler, EvHandlerState0) of
				{Error={error, _}, EvHandlerState} -> {handle_ret(Error, State0), EvHandlerState};
				{State, EvHandlerState} -> parse(Rest, State, EvHandler, EvHandlerState)
			end;
		more ->
			{handle_ret({state, State0#http2_state{buffer=Data}}, State0), EvHandlerState0};
		%% Any error in the preface is converted to this specific error
		%% to make debugging the problem easier (it's the server's fault).
		_ ->
			Reason = case Data of
				<<"HTTP/1",_/bits>> ->
					'Invalid connection preface received. Appears to be an HTTP/1 response? (RFC7540 3.5)';
				_ ->
					'Invalid connection preface received. (RFC7540 3.5)'
			end,
			{handle_ret(connection_error(State0, {connection_error, protocol_error, Reason}), State0),
				EvHandlerState0}
	end;
parse(Data, State0=#http2_state{status=Status, http2_machine=HTTP2Machine, streams=Streams},
		EvHandler, EvHandlerState0) ->
	MaxFrameSize = cow_http2_machine:get_local_setting(max_frame_size, HTTP2Machine),
	case cow_http2:parse(Data, MaxFrameSize) of
		{ok, Frame, Rest} ->
			case frame(State0, Frame, EvHandler, EvHandlerState0) of
				{Error={error, _}, EvHandlerState} -> {handle_ret(Error, State0), EvHandlerState};
				{State, EvHandlerState} -> parse(Rest, State, EvHandler, EvHandlerState)
			end;
		{ignore, Rest} ->
			case ignored_frame(State0) of
				Error = {error, _} -> {handle_ret(Error, State0), EvHandlerState0};
				State -> parse(Rest, State, EvHandler, EvHandlerState0)
			end;
		{stream_error, StreamID, Reason, Human, Rest} ->
			parse(Rest, reset_stream(State0, StreamID, {stream_error, Reason, Human}),
				EvHandler, EvHandlerState0);
		Error = {connection_error, _, _} ->
			{handle_ret(connection_error(State0, Error), State0), EvHandlerState0};
		%% If we both received and sent a GOAWAY frame and there are no streams
		%% currently running, we can close the connection immediately.
		more when Status =/= connected, Streams =:= #{} ->
			{handle_ret([{state, State0#http2_state{buffer=Data, status=closing}}, close], State0),
				EvHandlerState0};
		%% Otherwise we enter the closing state.
		more when Status =:= goaway ->
			{handle_ret([{state, State0#http2_state{buffer=Data, status=closing}}, closing(State0)], State0),
				EvHandlerState0};
		more ->
			{handle_ret({state, State0#http2_state{buffer=Data}}, State0), EvHandlerState0}
	end.

%% Frames received.

frame(State=#http2_state{http2_machine=HTTP2Machine0}, Frame, EvHandler, EvHandlerState0) ->
	EvHandlerState = if
		element(1, Frame) =:= headers; element(1, Frame) =:= push_promise ->
			EvStreamID = element(2, Frame),
			case cow_http2_machine:get_stream_remote_state(EvStreamID, HTTP2Machine0) of
				{ok, idle} ->
					#stream{ref=StreamRef, reply_to=ReplyTo} = get_stream_by_id(State, EvStreamID),
					EvCallback = case element(1, Frame) of
						headers -> response_start;
						push_promise -> push_promise_start
					end,
					EvHandler:EvCallback(#{
						stream_ref => StreamRef,
						reply_to => ReplyTo
					}, EvHandlerState0);
				%% Trailers or invalid header frame.
				_ ->
					EvHandlerState0
			end;
		true ->
			EvHandlerState0
	end,
	case cow_http2_machine:frame(Frame, HTTP2Machine0) of
		%% We only update the connection's window when receiving a lingering data frame.
		{ok, HTTP2Machine} when element(1, Frame) =:= data ->
			{update_window(State#http2_state{http2_machine=HTTP2Machine}), EvHandlerState};
		{ok, HTTP2Machine} ->
			{maybe_ack(State#http2_state{http2_machine=HTTP2Machine}, Frame),
				EvHandlerState};
		{ok, {data, StreamID, IsFin, Data}, HTTP2Machine} ->
			data_frame(State#http2_state{http2_machine=HTTP2Machine}, StreamID, IsFin, Data,
				EvHandler, EvHandlerState);
		{ok, {headers, StreamID, IsFin, Headers, PseudoHeaders, BodyLen}, HTTP2Machine} ->
			headers_frame(State#http2_state{http2_machine=HTTP2Machine},
				StreamID, IsFin, Headers, PseudoHeaders, BodyLen,
				EvHandler, EvHandlerState);
		{ok, {trailers, StreamID, Trailers}, HTTP2Machine} ->
			trailers_frame(State#http2_state{http2_machine=HTTP2Machine},
				StreamID, Trailers, EvHandler, EvHandlerState);
		{ok, {rst_stream, StreamID, Reason}, HTTP2Machine} ->
			rst_stream_frame(State#http2_state{http2_machine=HTTP2Machine},
				StreamID, Reason, EvHandler, EvHandlerState);
		{ok, {push_promise, StreamID, PromisedStreamID, Headers, PseudoHeaders}, HTTP2Machine} ->
			push_promise_frame(State#http2_state{http2_machine=HTTP2Machine},
				StreamID, PromisedStreamID, Headers, PseudoHeaders,
				EvHandler, EvHandlerState);
		{ok, GoAway={goaway, _, _, _}, HTTP2Machine} ->
			{goaway(State#http2_state{http2_machine=HTTP2Machine}, GoAway),
				EvHandlerState};
		{send, SendData, HTTP2Machine} ->
			send_data(maybe_ack(State#http2_state{http2_machine=HTTP2Machine}, Frame), SendData,
				EvHandler, EvHandlerState);
		{error, {stream_error, StreamID, Reason, Human}, HTTP2Machine} ->
			{reset_stream(State#http2_state{http2_machine=HTTP2Machine},
				StreamID, {stream_error, Reason, Human}),
				EvHandlerState};
		{error, Error={connection_error, _, _}, HTTP2Machine} ->
			{connection_error(State#http2_state{http2_machine=HTTP2Machine}, Error),
				EvHandlerState}
	end.

maybe_ack(State=#http2_state{socket=Socket, transport=Transport}, Frame) ->
	case Frame of
		{settings, _} -> Transport:send(Socket, cow_http2:settings_ack());
		{ping, Opaque} -> Transport:send(Socket, cow_http2:ping_ack(Opaque));
		_ -> ok
	end,
	State.

data_frame(State, StreamID, IsFin, Data, EvHandler, EvHandlerState0) ->
	case get_stream_by_id(State, StreamID) of
		Stream=#stream{tunnel=undefined} ->
			data_frame(State, StreamID, IsFin, Data, EvHandler, EvHandlerState0, Stream);
		#stream{ref=StreamRef, reply_to=ReplyTo,
				tunnel={_Protocol, _ProtoState, #{tls_proxy_pid := ProxyPid}}} ->
			%% When we receive a DATA frame that contains TLS-encoded data,
			%% we must first forward it to the ProxyPid to be decoded. The
			%% Gun process will receive it back as a tls_proxy_http2_connect
			%% message and forward it to the right stream via the handle_continue
			%% callback.
			OriginSocket = #{
				gun_pid => self(),
				reply_to => ReplyTo,
				stream_ref => stream_ref(State, StreamRef)
			},
			ProxyPid ! {tls_proxy_http2_connect, OriginSocket, Data},
			%% @todo What about IsFin?
			{State, EvHandlerState0};
		Stream=#stream{tunnel={Protocol, ProtoState0, TunnelInfo}} ->
			{Commands, EvHandlerState} = Protocol:handle(Data, ProtoState0, EvHandler, EvHandlerState0),
			{tunnel_commands(Commands, Stream, Protocol, TunnelInfo, State), EvHandlerState}
	end.

tunnel_commands(Command, Stream, Protocol, TunnelInfo, State) when not is_list(Command) ->
	tunnel_commands([Command], Stream, Protocol, TunnelInfo, State);
tunnel_commands([], Stream, _, _, State) ->
	store_stream(State, Stream);
tunnel_commands([{state, ProtoState}|Tail], Stream, Protocol, TunnelInfo, State) ->
	tunnel_commands(Tail, Stream#stream{tunnel={Protocol, ProtoState, TunnelInfo}},
		Protocol, TunnelInfo, State);
tunnel_commands([SetCookie={set_cookie, _, _, _, _}|Tail], Stream, Protocol, TunnelInfo,
		State=#http2_state{commands_queue=Queue}) ->
	tunnel_commands(Tail, Stream, Protocol, TunnelInfo,
		State#http2_state{commands_queue=[SetCookie|Queue]});
tunnel_commands([{origin, _, NewHost, NewPort, Type}|Tail], Stream, Protocol, TunnelInfo, State) ->
%% @todo Event?
	tunnel_commands(Tail, Stream, Protocol, TunnelInfo#{
		origin_host => NewHost,
		origin_port => NewPort,
		intermediaries => [#{
			type => Type,
			host => maps:get(origin_host, TunnelInfo),
			port => maps:get(origin_port, TunnelInfo),
			transport => tcp, %% @todo
			protocol => Protocol:name()
		}|maps:get(intermediaries, TunnelInfo, [])]
	}, State);
tunnel_commands([{switch_protocol, NewProtocol, ReplyTo}|Tail], Stream=#stream{ref=StreamRef},
		_CurrentProtocol, TunnelInfo, State=#http2_state{opts=Opts}) ->
	{Protocol, ProtoOpts} = gun_protocols:handler_and_opts(NewProtocol, Opts),
	OriginSocket = #{
		gun_pid => self(),
		reply_to => ReplyTo,
		stream_ref => stream_ref(State, StreamRef)
	},
	OriginTransport = gun_tcp_proxy,
	{_, ProtoState} = Protocol:init(ReplyTo, OriginSocket, OriginTransport, ProtoOpts),
%% @todo	EvHandlerState = EvHandler:protocol_changed(#{protocol => Protocol:name()}, EvHandlerState0),
	tunnel_commands([{state, ProtoState}|Tail], Stream, Protocol, TunnelInfo, State);
tunnel_commands([{active, true}|Tail], Stream, Protocol, TunnelInfo, State) ->
	tunnel_commands(Tail, Stream, Protocol, TunnelInfo, State).

data_frame(State0, StreamID, IsFin, Data, EvHandler, EvHandlerState0,
		Stream=#stream{ref=StreamRef, reply_to=ReplyTo, flow=Flow0, handler_state=Handlers0}) ->
	{ok, Dec, Handlers} = gun_content_handler:handle(IsFin, Data, Handlers0),
	Flow = case Flow0 of
		infinity -> infinity;
		_ -> Flow0 - Dec
	end,
	State1 = store_stream(State0, Stream#stream{flow=Flow, handler_state=Handlers}),
	{State, EvHandlerState} = case byte_size(Data) of
		%% We do not send a WINDOW_UPDATE if the DATA frame was of size 0.
		0 when IsFin =:= fin ->
			EvHandlerState1 = EvHandler:response_end(#{
				stream_ref => StreamRef,
				reply_to => ReplyTo
			}, EvHandlerState0),
			{State1, EvHandlerState1};
		0 ->
			{State1, EvHandlerState0};
		_ ->
			%% We do not send a stream WINDOW_UPDATE when the flow control kicks in
			%% (it'll be sent when the flow recovers) or for the last DATA frame.
			case IsFin of
				nofin when Flow =< 0 ->
					{update_window(State1), EvHandlerState0};
				nofin ->
					{update_window(State1, StreamID), EvHandlerState0};
				fin ->
					EvHandlerState1 = EvHandler:response_end(#{
						stream_ref => StreamRef,
						reply_to => ReplyTo
					}, EvHandlerState0),
					{update_window(State1), EvHandlerState1}
			end
	end,
	{maybe_delete_stream(State, StreamID, remote, IsFin), EvHandlerState}.

headers_frame(State0=#http2_state{opts=Opts, content_handlers=Handlers0, commands_queue=Commands},
		StreamID, IsFin, Headers, #{status := Status}, _BodyLen,
		EvHandler, EvHandlerState0) ->
	Stream = get_stream_by_id(State0, StreamID),
	#stream{
		ref=StreamRef,
		reply_to=ReplyTo,
		authority=Authority,
		path=Path,
		tunnel=Tunnel
	} = Stream,
	State = State0#http2_state{commands_queue=[{set_cookie, Authority, Path, Status, Headers}|Commands]},
	if
		Status >= 100, Status =< 199 ->
			ReplyTo ! {gun_inform, self(), stream_ref(State, StreamRef), Status, Headers},
			EvHandlerState = EvHandler:response_inform(#{
				stream_ref => StreamRef,
				reply_to => ReplyTo,
				status => Status,
				headers => Headers
			}, EvHandlerState0),
			{State, EvHandlerState};
		Status >= 200, Status =< 299, element(1, Tunnel) =:= setup ->
			{setup, Destination=#{host := DestHost, port := DestPort}, TunnelInfo} = Tunnel,
			%% In the case of CONNECT responses the RealStreamRef is found in TunnelInfo.
			%% We therefore do not need to call stream_ref/2.
			RealStreamRef = stream_ref(State, StreamRef),
			ReplyTo ! {gun_response, self(), RealStreamRef, IsFin, Status, Headers},
			EvHandlerState = EvHandler:response_headers(#{
				stream_ref => RealStreamRef,
				reply_to => ReplyTo,
				status => Status,
				headers => Headers
			}, EvHandlerState0),
			OriginSocket = #{
				gun_pid => self(),
				reply_to => ReplyTo,
				stream_ref => RealStreamRef
			},
			case Destination of
				#{transport := tls} ->
					Protocols = maps:get(protocols, Destination, [http2, http]),
					TLSOpts = gun:ensure_alpn_sni(Protocols, maps:get(tls_opts, Destination, []), DestHost),
					TLSTimeout = maps:get(tls_handshake_timeout, Destination, infinity),
%					HandshakeEvent = #{
%						stream_ref => StreamRef,
%						reply_to => ReplyTo,
%						tls_opts => maps:get(tls_opts, Destination, []),
%						timeout => maps:get(tls_handshake_timeout, Destination, infinity)
%					},
%tls_handshake(internal, {tls_handshake,
%		HandshakeEvent0=#{tls_opts := TLSOpts0, timeout := TLSTimeout}, Protocols, ReplyTo},
%		State=#state{socket=Socket, transport=Transport, origin_host=OriginHost, origin_port=OriginPort,
%		event_handler=EvHandler, event_handler_state=EvHandlerState0}) ->
%	HandshakeEvent = HandshakeEvent0#{
%		tls_opts => TLSOpts,
%		socket => Socket
%	},
%	EvHandlerState = EvHandler:tls_handshake_start(HandshakeEvent, EvHandlerState0),
					HandshakeEvent = undefined,
					{ok, ProxyPid} = gun_tls_proxy:start_link(DestHost, DestPort,
						TLSOpts, TLSTimeout, OriginSocket, gun_tls_proxy_http2_connect,
						%% @todo ?
%						{HandshakeEvent, Protocols, ReplyTo}),
						{handle_continue, RealStreamRef, HandshakeEvent, Protocols}),
%	commands([{switch_transport, gun_tls_proxy, ProxyPid}], State#state{
%		socket=ProxyPid, transport=gun_tls_proxy, event_handler_state=EvHandlerState});
					%% @todo What about keepalive?
					{store_stream(State, Stream#stream{tunnel={tls_handshake, Destination,
						TunnelInfo#{origin_host => DestHost, origin_port => DestPort,
							%% @todo Fine having it, but we want the socket pid to simulate active.
							tls_proxy_pid => ProxyPid}}}),
						EvHandlerState};
				_ ->
					[NewProtocol] = maps:get(protocols, Destination, [http]),
					{Protocol, ProtoOpts} = gun_protocols:handler_and_opts(NewProtocol, Opts),
					%% @todo What about the StateName returned?
					{_, ProtoState} = Protocol:init(ReplyTo, OriginSocket, gun_tcp_proxy, ProtoOpts#{stream_ref => RealStreamRef}),
					%% @todo EvHandlerState = EvHandler:protocol_changed(#{protocol => Protocol:name()}, EvHandlerState0),
					%% @todo What about keepalive?
					ReplyTo ! {gun_tunnel_up, self(), RealStreamRef, Protocol:name()},
					{store_stream(State, Stream#stream{tunnel={Protocol, ProtoState,
						TunnelInfo#{origin_host => DestHost, origin_port => DestPort}}}),
						EvHandlerState}
			end;
		true ->
			ReplyTo ! {gun_response, self(), stream_ref(State, StreamRef), IsFin, Status, Headers},
			EvHandlerState1 = EvHandler:response_headers(#{
				stream_ref => StreamRef,
				reply_to => ReplyTo,
				status => Status,
				headers => Headers
			}, EvHandlerState0),
			{Handlers, EvHandlerState} = case IsFin of
				fin ->
					EvHandlerState2 = EvHandler:response_end(#{
						stream_ref => StreamRef,
						reply_to => ReplyTo
					}, EvHandlerState1),
					{undefined, EvHandlerState2};
				nofin ->
					{gun_content_handler:init(ReplyTo, StreamRef,
						Status, Headers, Handlers0), EvHandlerState1}
			end,
			%% @todo Disable the tunnel if any.
			{maybe_delete_stream(store_stream(State, Stream#stream{handler_state=Handlers}),
				StreamID, remote, IsFin),
				EvHandlerState}
	end.

trailers_frame(State, StreamID, Trailers, EvHandler, EvHandlerState0) ->
	#stream{ref=StreamRef, reply_to=ReplyTo} = get_stream_by_id(State, StreamID),
	%% @todo We probably want to pass this to gun_content_handler?
	ReplyTo ! {gun_trailers, self(), stream_ref(State, StreamRef), Trailers},
	ResponseEvent = #{
		stream_ref => StreamRef,
		reply_to => ReplyTo
	},
	EvHandlerState1 = EvHandler:response_trailers(ResponseEvent#{headers => Trailers}, EvHandlerState0),
	EvHandlerState = EvHandler:response_end(ResponseEvent, EvHandlerState1),
	{maybe_delete_stream(State, StreamID, remote, fin), EvHandlerState}.

rst_stream_frame(State0, StreamID, Reason, EvHandler, EvHandlerState0) ->
	case take_stream(State0, StreamID) of
		{#stream{ref=StreamRef, reply_to=ReplyTo}, State} ->
			ReplyTo ! {gun_error, self(), stream_ref(State0, StreamRef),
				{stream_error, Reason, 'Stream reset by server.'}},
			EvHandlerState = EvHandler:cancel(#{
				stream_ref => StreamRef,
				reply_to => ReplyTo,
				endpoint => remote,
				reason => Reason
			}, EvHandlerState0),
			{State, EvHandlerState};
		error ->
			{State0, EvHandlerState0}
	end.

%% Pushed streams receive the same initial flow value as the parent stream.
push_promise_frame(State=#http2_state{socket=Socket, transport=Transport,
		status=Status, http2_machine=HTTP2Machine0},
		StreamID, PromisedStreamID, Headers, #{
			method := Method, scheme := Scheme,
			authority := Authority, path := Path},
		EvHandler, EvHandlerState0) ->
	#stream{ref=StreamRef, reply_to=ReplyTo, flow=InitialFlow} = get_stream_by_id(State, StreamID),
	PromisedStreamRef = make_ref(),
	URI = iolist_to_binary([Scheme, <<"://">>, Authority, Path]),
	PushPromiseEvent0 = #{
		stream_ref => StreamRef,
		reply_to => ReplyTo,
		method => Method,
		uri => URI,
		headers => Headers
	},
	PushPromiseEvent = case Status of
		connected ->
			ReplyTo ! {gun_push, self(), stream_ref(State, StreamRef), PromisedStreamRef, Method, URI, Headers},
			PushPromiseEvent0#{promised_stream_ref => PromisedStreamRef};
		_ ->
			PushPromiseEvent0
	end,
	EvHandlerState = EvHandler:push_promise_end(PushPromiseEvent, EvHandlerState0),
	case Status of
		connected ->
			NewStream = #stream{id=PromisedStreamID, ref=PromisedStreamRef,
				reply_to=ReplyTo, flow=InitialFlow, authority=Authority, path=Path},
			{create_stream(State, NewStream), EvHandlerState};
		%% We cancel the push_promise immediately when we are shutting down.
		_ ->
			{ok, HTTP2Machine} = cow_http2_machine:reset_stream(PromisedStreamID, HTTP2Machine0),
			Transport:send(Socket, cow_http2:rst_stream(PromisedStreamID, cancel)),
			{State#http2_state{http2_machine=HTTP2Machine}, EvHandlerState}
	end.

ignored_frame(State=#http2_state{http2_machine=HTTP2Machine0}) ->
	case cow_http2_machine:ignored_frame(HTTP2Machine0) of
		{ok, HTTP2Machine} ->
			State#http2_state{http2_machine=HTTP2Machine};
		{error, Error={connection_error, _, _}, HTTP2Machine} ->
			connection_error(State#http2_state{http2_machine=HTTP2Machine}, Error)
	end.

%% Continue handling or sending the data.
handle_continue(StreamRef, Msg, State=#http2_state{opts=Opts}, EvHandler, EvHandlerState0)
		when is_reference(StreamRef) ->
	case get_stream_by_ref(State, StreamRef) of
		Stream=#stream{id=StreamID, reply_to=ReplyTo,
				tunnel={tls_handshake, Destination, TunnelInfo=#{tls_proxy_pid := ProxyPid}}} ->
			case Msg of
				{gun_tls_proxy, ProxyPid, {ok, Negotiated},
						{handle_continue, _, _HandshakeEvent, Protocols}} ->
					#{host := DestHost, port := DestPort} = Destination,
					RealStreamRef = stream_ref(State, StreamRef),
					NewProtocol = gun_protocols:negotiated(Negotiated, Protocols),
%					EvHandlerState = EvHandler:tls_handshake_end(HandshakeEvent#{
%						socket => Socket,
%						protocol => NewProtocol
%					}, EvHandlerState0),
					OriginSocket = #{
						gun_pid => self(),
						reply_to => ReplyTo,
						stream_ref => RealStreamRef
					},
					{Protocol, ProtoOpts} = gun_protocols:handler_and_opts(NewProtocol, Opts),
					{_, ProtoState} = Protocol:init(ReplyTo, OriginSocket, gun_tcp_proxy,
						ProtoOpts#{stream_ref => RealStreamRef}),
					ReplyTo ! {gun_tunnel_up, self(), RealStreamRef, Protocol:name()},
					{{state, store_stream(State, Stream#stream{tunnel={Protocol, ProtoState,
						TunnelInfo#{origin_host => DestHost, origin_port => DestPort}}})},
						EvHandlerState0};
				{gun_tls_proxy, ProxyPid, {error, _Reason},
						{handle_continue, _, _HandshakeEvent, _}} ->
%					EvHandlerState = EvHandler:tls_handshake_end(HandshakeEvent#{
%						error => Reason
%					}, EvHandlerState0),
%% @todo
%   The TCP connection can be closed by either peer.  The END_STREAM flag
%   on a DATA frame is treated as being equivalent to the TCP FIN bit.  A
%   client is expected to send a DATA frame with the END_STREAM flag set
%   after receiving a frame bearing the END_STREAM flag.  A proxy that
%   receives a DATA frame with the END_STREAM flag set sends the attached
%   data with the FIN bit set on the last TCP segment.  A proxy that
%   receives a TCP segment with the FIN bit set sends a DATA frame with
%   the END_STREAM flag set.  Note that the final TCP segment or DATA
%   frame could be empty.
					{{state, State}, EvHandlerState0};
				%% Data that must be sent as a DATA frame.
				{data, ReplyTo, _, IsFin, Data} ->
					{State1, EvHandlerState} = maybe_send_data(State, StreamID, IsFin, Data, EvHandler, EvHandlerState0),
					{{state, State1}, EvHandlerState}
			end;
		Stream=#stream{id=StreamID, tunnel={Protocol, ProtoState0, TunnelInfo=#{tls_proxy_pid := ProxyPid}}} ->
			case Msg of
				%% Data that was received and decrypted.
				{tls_proxy, ProxyPid, Data} ->
					{Commands, EvHandlerState} = Protocol:handle(Data, ProtoState0, EvHandler, EvHandlerState0),
					{{state, tunnel_commands(Commands, Stream, Protocol, TunnelInfo, State)}, EvHandlerState};
				%% @todo What to do about those?
				{tls_proxy_closed, ProxyPid} ->
					todo;
				{tls_proxy_error, ProxyPid, _Reason} ->
					todo;
				%% Data that must be sent as a DATA frame.
				{data, _, _, IsFin, Data} ->
					{State1, EvHandlerState} = maybe_send_data(State, StreamID, IsFin, Data, EvHandler, EvHandlerState0),
					{{state, State1}, EvHandlerState}
			end
%% @todo Is this possible?
%		error ->
%			{error_stream_not_found(State, StreamRef, ReplyTo), EvHandlerState0}
	end;
%% Tunneled data.
handle_continue([StreamRef|Tail], Msg, State, EvHandler, EvHandlerState0) ->
	case get_stream_by_ref(State, StreamRef) of
		Stream=#stream{tunnel={Proto, ProtoState0, TunnelInfo}} ->
			{ProtoState, EvHandlerState} = Proto:handle_continue(normalize_stream_ref(Tail),
				Msg, ProtoState0, EvHandler, EvHandlerState0),
			{store_stream(State, Stream#stream{tunnel={Proto, ProtoState, TunnelInfo}}), EvHandlerState}%;
		%% The stream may have ended while TLS was being decoded. @todo What should we do?
%		error ->
%			{error_stream_not_found(State, StreamRef, ReplyTo), EvHandlerState0}
	end.

update_flow(State, _ReplyTo, StreamRef, Inc) ->
	case get_stream_by_ref(State, StreamRef) of
		Stream=#stream{id=StreamID, flow=Flow0} ->
			Flow = case Flow0 of
				infinity -> infinity;
				_ -> Flow0 + Inc
			end,
			if
				%% Flow is active again, update the stream's window.
				Flow0 =< 0, Flow > 0 ->
					{state, update_window(store_stream(State,
						Stream#stream{flow=Flow}), StreamID)};
				true ->
					{state, store_stream(State, Stream#stream{flow=Flow})}
			end;
		error ->
			[]
	end.

%% Only update the connection's window.
update_window(State=#http2_state{socket=Socket, transport=Transport,
		opts=#{initial_connection_window_size := ConnWindow}, http2_machine=HTTP2Machine0}) ->
	case cow_http2_machine:ensure_window(ConnWindow, HTTP2Machine0) of
		ok ->
			State;
		{ok, Increment, HTTP2Machine} ->
			Transport:send(Socket, cow_http2:window_update(Increment)),
			State#http2_state{http2_machine=HTTP2Machine}
	end.

%% Update both the connection and the stream's window.
update_window(State=#http2_state{socket=Socket, transport=Transport,
		opts=#{initial_connection_window_size := ConnWindow, initial_stream_window_size := StreamWindow},
		http2_machine=HTTP2Machine0}, StreamID) ->
	{Data1, HTTP2Machine2} = case cow_http2_machine:ensure_window(ConnWindow, HTTP2Machine0) of
		ok -> {<<>>, HTTP2Machine0};
		{ok, Increment1, HTTP2Machine1} -> {cow_http2:window_update(Increment1), HTTP2Machine1}
	end,
	{Data2, HTTP2Machine} = case cow_http2_machine:ensure_window(StreamID, StreamWindow, HTTP2Machine2) of
		ok -> {<<>>, HTTP2Machine2};
		{ok, Increment2, HTTP2Machine3} -> {cow_http2:window_update(StreamID, Increment2), HTTP2Machine3}
	end,
	case {Data1, Data2} of
		{<<>>, <<>>} -> ok;
		_ -> Transport:send(Socket, [Data1, Data2])
	end,
	State#http2_state{http2_machine=HTTP2Machine}.

%% We may have to cancel streams even if we receive multiple
%% GOAWAY frames as the LastStreamID value may be lower than
%% the one previously received.
goaway(State0=#http2_state{socket=Socket, transport=Transport, http2_machine=HTTP2Machine,
		status=Status, streams=Streams0, stream_refs=Refs}, {goaway, LastStreamID, Reason, _}) ->
	{Streams, RemovedRefs} = goaway_streams(State0, maps:to_list(Streams0), LastStreamID,
		{goaway, Reason, 'The connection is going away.'}, [], []),
	State = State0#http2_state{
		streams=maps:from_list(Streams),
		stream_refs=maps:without(RemovedRefs, Refs)
	},
	case Status of
		connected ->
			Transport:send(Socket, cow_http2:goaway(
				cow_http2_machine:get_last_streamid(HTTP2Machine),
				no_error, <<>>)),
			State#http2_state{status=goaway};
		_ ->
			State
	end.

%% Cancel server-initiated streams that are above LastStreamID.
goaway_streams(_, [], _, _, Acc, RefsAcc) ->
	{Acc, RefsAcc};
goaway_streams(State, [{StreamID, Stream=#stream{ref=StreamRef}}|Tail], LastStreamID, Reason, Acc, RefsAcc)
		when StreamID > LastStreamID, (StreamID rem 2) =:= 1 ->
	close_stream(State, Stream, Reason),
	goaway_streams(State, Tail, LastStreamID, Reason, Acc, [StreamRef|RefsAcc]);
goaway_streams(State, [StreamWithID|Tail], LastStreamID, Reason, Acc, RefsAcc) ->
	goaway_streams(State, Tail, LastStreamID, Reason, [StreamWithID|Acc], RefsAcc).

%% We are already closing, do nothing.
closing(_, #http2_state{status=closing}, _, EvHandlerState) ->
	{[], EvHandlerState};
closing(Reason0, State=#http2_state{socket=Socket, transport=Transport,
		http2_machine=HTTP2Machine}, _, EvHandlerState) ->
	Reason = case Reason0 of
		normal -> no_error;
		owner_down -> no_error;
		_ -> internal_error
	end,
	Transport:send(Socket, cow_http2:goaway(
		cow_http2_machine:get_last_streamid(HTTP2Machine),
		Reason, <<>>)),
	{[
		{state, State#http2_state{status=closing}},
		closing(State)
	], EvHandlerState}.

closing(#http2_state{opts=Opts}) ->
	Timeout = maps:get(closing_timeout, Opts, 15000),
	{closing, Timeout}.

close(Reason0, State=#http2_state{streams=Streams}, _, EvHandlerState) ->
	Reason = close_reason(Reason0),
	_ = maps:fold(fun(_, Stream, _) ->
		close_stream(State, Stream, Reason)
	end, [], Streams),
	EvHandlerState.

close_reason(closed) -> closed;
close_reason(Reason) -> {closed, Reason}.

%% @todo Do we want an event for this?
close_stream(State, #stream{ref=StreamRef, reply_to=ReplyTo}, Reason) ->
	ReplyTo ! {gun_error, self(), stream_ref(State, StreamRef), Reason},
	ok.

keepalive(State=#http2_state{socket=Socket, transport=Transport}, _, EvHandlerState) ->
	Transport:send(Socket, cow_http2:ping(0)),
	{State, EvHandlerState}.

%% @todo tunnel
headers(State=#http2_state{socket=Socket, transport=Transport, opts=Opts,
		http2_machine=HTTP2Machine0}, StreamRef, ReplyTo, Method, Host, Port,
		Path, Headers0, InitialFlow0, EvHandler, EvHandlerState0) ->
	{ok, StreamID, HTTP2Machine1} = cow_http2_machine:init_stream(
		iolist_to_binary(Method), HTTP2Machine0),
	{ok, PseudoHeaders, Headers} = prepare_headers(State, Method, Host, Port, Path, Headers0),
	Authority = maps:get(authority, PseudoHeaders),
	RequestEvent = #{
		stream_ref => StreamRef,
		reply_to => ReplyTo,
		function => ?FUNCTION_NAME,
		method => Method,
		authority => Authority,
		path => Path,
		headers => Headers
	},
	EvHandlerState1 = EvHandler:request_start(RequestEvent, EvHandlerState0),
	{ok, IsFin, HeaderBlock, HTTP2Machine} = cow_http2_machine:prepare_headers(
		StreamID, HTTP2Machine1, nofin, PseudoHeaders, Headers),
	Transport:send(Socket, cow_http2:headers(StreamID, IsFin, HeaderBlock)),
	EvHandlerState = EvHandler:request_headers(RequestEvent, EvHandlerState1),
	InitialFlow = initial_flow(InitialFlow0, Opts),
	Stream = #stream{id=StreamID, ref=StreamRef, reply_to=ReplyTo, flow=InitialFlow,
		authority=Authority, path=Path},
	{create_stream(State#http2_state{http2_machine=HTTP2Machine}, Stream), EvHandlerState}.

request(State0=#http2_state{socket=Socket, transport=Transport, opts=Opts,
		http2_machine=HTTP2Machine0}, StreamRef, ReplyTo, Method, Host, Port,
		Path, Headers0, Body, InitialFlow0, EvHandler, EvHandlerState0)
		when is_reference(StreamRef) ->
	Headers1 = lists:keystore(<<"content-length">>, 1, Headers0,
		{<<"content-length">>, integer_to_binary(iolist_size(Body))}),
	{ok, StreamID, HTTP2Machine1} = cow_http2_machine:init_stream(
		iolist_to_binary(Method), HTTP2Machine0),
	{ok, PseudoHeaders, Headers} = prepare_headers(State0, Method, Host, Port, Path, Headers1),
	Authority = maps:get(authority, PseudoHeaders),
	RequestEvent = #{
		stream_ref => StreamRef,
		reply_to => ReplyTo,
		function => ?FUNCTION_NAME,
		method => Method,
		authority => Authority,
		path => Path,
		headers => Headers
	},
	EvHandlerState1 = EvHandler:request_start(RequestEvent, EvHandlerState0),
	IsFin0 = case iolist_size(Body) of
		0 -> fin;
		_ -> nofin
	end,
	{ok, IsFin, HeaderBlock, HTTP2Machine} = cow_http2_machine:prepare_headers(
		StreamID, HTTP2Machine1, IsFin0, PseudoHeaders, Headers),
	Transport:send(Socket, cow_http2:headers(StreamID, IsFin, HeaderBlock)),
	EvHandlerState = EvHandler:request_headers(RequestEvent, EvHandlerState1),
	InitialFlow = initial_flow(InitialFlow0, Opts),
	Stream = #stream{id=StreamID, ref=StreamRef, reply_to=ReplyTo, flow=InitialFlow,
		authority=Authority, path=Path},
	State = create_stream(State0#http2_state{http2_machine=HTTP2Machine}, Stream),
	case IsFin of
		fin ->
			RequestEndEvent = #{
				stream_ref => StreamRef,
				reply_to => ReplyTo
			},
			{State, EvHandler:request_end(RequestEndEvent, EvHandlerState)};
		nofin ->
			maybe_send_data(State, StreamID, fin, Body, EvHandler, EvHandlerState)
	end;
%% Tunneled request.
%%
%% We call Proto:request in a loop until we get to a non-CONNECT stream.
%% When the transport is gun_tls_proxy we receive the TLS data
%% as a 'data' cast; when gun_tcp_proxy we receive the 'data' cast
%% directly. The 'data' cast contains the tunnel for the StreamRef.
%% The tunnel is given as the socket and the gun_tls_proxy out_socket
%% is always a gun_tcp_proxy that sends a 'data' cast.
request(State, [StreamRef|Tail], ReplyTo, Method, _Host, _Port,
		Path, Headers, Body, InitialFlow, EvHandler, EvHandlerState0) ->
	case get_stream_by_ref(State, StreamRef) of
		%% @todo We should send an error to the user if the stream isn't ready.
		Stream=#stream{tunnel={Proto, ProtoState0, TunnelInfo=#{
				origin_host := OriginHost, origin_port := OriginPort}}} ->
			%% @todo So the event is probably not giving the right StreamRef?
			{ProtoState, EvHandlerState} = Proto:request(ProtoState0, normalize_stream_ref(Tail),
				ReplyTo, Method, OriginHost, OriginPort, Path, Headers, Body,
				InitialFlow, EvHandler, EvHandlerState0),
			{store_stream(State, Stream#stream{tunnel={Proto, ProtoState, TunnelInfo}}), EvHandlerState};
		#stream{tunnel=undefined} ->
			ReplyTo ! {gun_error, self(), stream_ref(State, StreamRef), {badstate,
				"The stream is not a tunnel."}},
			{State, EvHandlerState0};
		error ->
			{error_stream_not_found(State, StreamRef, ReplyTo), EvHandlerState0}
	end.

	%% get the ultimate stream by querying the #stream{} until we get the last one
	%% call Proto:request in that stream
	%% receive a {data, ...} back with the Tunnel for the StreamRef
		%% if gun_tls_proxy then we get the wrapped TLS data
		%% otherwise we get the data directly
	%% handle the data in the same way as normal; data follows the same scenario
	%% until we get a {data, ...} for the top-level stream

	%% What about data we receive from the socket?
	%%
	%% we get DATA with a StreamID for the CONNECT, we see it's CONNECT so we forward to Proto:data

initial_flow(infinity, #{flow := InitialFlow}) -> InitialFlow;
initial_flow(InitialFlow, _) -> InitialFlow.

prepare_headers(#http2_state{transport=Transport}, Method, Host0, Port, Path, Headers0) ->
	Authority = case lists:keyfind(<<"host">>, 1, Headers0) of
		{_, Host} -> Host;
		_ -> gun_http:host_header(Transport, Host0, Port)
	end,
	%% @todo We also must remove any header found in the connection header.
	%% @todo Much of this is duplicated in cow_http2_machine; sort things out.
	Headers =
		lists:keydelete(<<"host">>, 1,
		lists:keydelete(<<"connection">>, 1,
		lists:keydelete(<<"keep-alive">>, 1,
		lists:keydelete(<<"proxy-connection">>, 1,
		lists:keydelete(<<"transfer-encoding">>, 1,
		lists:keydelete(<<"upgrade">>, 1, Headers0)))))),
	PseudoHeaders = #{
		method => Method,
		scheme => case Transport of
			gun_tls -> <<"https">>;
			gun_tls_proxy -> <<"https">>;
			gun_tcp -> <<"http">>;
			gun_tcp_proxy -> <<"http">>
		end,
		authority => Authority,
		path => Path
	},
	{ok, PseudoHeaders, Headers}.

normalize_stream_ref([StreamRef]) -> StreamRef;
normalize_stream_ref(StreamRef) -> StreamRef.

data(State=#http2_state{http2_machine=HTTP2Machine}, StreamRef, ReplyTo, IsFin, Data,
		EvHandler, EvHandlerState) when is_reference(StreamRef) ->
	case get_stream_by_ref(State, StreamRef) of
		#stream{id=StreamID, tunnel=Tunnel} ->
			case cow_http2_machine:get_stream_local_state(StreamID, HTTP2Machine) of
				{ok, fin, _} ->
					{error_stream_closed(State, StreamRef, ReplyTo), EvHandlerState};
				{ok, _, fin} ->
					{error_stream_closed(State, StreamRef, ReplyTo), EvHandlerState};
				{ok, _, _} ->
					case Tunnel of
						%% We need to encrypt the data before we can send it. We send it
						%% directly to the gun_tls_proxy process and then
						{_, _, #{tls_proxy_pid := ProxyPid}} ->
							ok = gun_tls_proxy:send(ProxyPid, Data),
							{State, EvHandlerState};
						_ ->
							maybe_send_data(State, StreamID, IsFin, Data, EvHandler, EvHandlerState)
					end
			end;
		error ->
			{error_stream_not_found(State, StreamRef, ReplyTo), EvHandlerState}
	end;
%% Tunneled data.
data(State, [StreamRef|Tail], ReplyTo, IsFin, Data, EvHandler, EvHandlerState0) ->
	case get_stream_by_ref(State, StreamRef) of
		Stream=#stream{tunnel={Proto, ProtoState0, TunnelInfo}} ->
			{ProtoState, EvHandlerState} = Proto:data(ProtoState0, normalize_stream_ref(Tail),
				ReplyTo, IsFin, Data, EvHandler, EvHandlerState0),
			{store_stream(State, Stream#stream{tunnel={Proto, ProtoState, TunnelInfo}}), EvHandlerState};
		#stream{tunnel=undefined} ->
			ReplyTo ! {gun_error, self(), stream_ref(State, StreamRef), {badstate,
				"The stream is not a tunnel."}},
			{State, EvHandlerState0};
		error ->
			{error_stream_not_found(State, StreamRef, ReplyTo), EvHandlerState0}
	end.

maybe_send_data(State=#http2_state{http2_machine=HTTP2Machine0}, StreamID, IsFin, Data0,
		EvHandler, EvHandlerState) ->
	Data = case is_tuple(Data0) of
		false -> {data, Data0};
		true -> Data0
	end,
	case cow_http2_machine:send_or_queue_data(StreamID, HTTP2Machine0, IsFin, Data) of
		{ok, HTTP2Machine} ->
			{State#http2_state{http2_machine=HTTP2Machine}, EvHandlerState};
		{send, SendData, HTTP2Machine} ->
			send_data(State#http2_state{http2_machine=HTTP2Machine}, SendData,
				EvHandler, EvHandlerState)
	end.

send_data(State, [], _, EvHandlerState) ->
	{State, EvHandlerState};
send_data(State0, [{StreamID, IsFin, SendData}|Tail], EvHandler, EvHandlerState0) ->
	{State, EvHandlerState} = send_data(State0, StreamID, IsFin, SendData, EvHandler, EvHandlerState0),
	send_data(State, Tail, EvHandler, EvHandlerState).

send_data(State0, StreamID, IsFin, [Data], EvHandler, EvHandlerState0) ->
	State = send_data_frame(State0, StreamID, IsFin, Data),
	EvHandlerState = case IsFin of
		nofin ->
			EvHandlerState0;
		fin ->
			#stream{ref=StreamRef, reply_to=ReplyTo} = get_stream_by_id(State, StreamID),
			RequestEndEvent = #{
				stream_ref => StreamRef,
				reply_to => ReplyTo
			},
			EvHandler:request_end(RequestEndEvent, EvHandlerState0)
	end,
	{maybe_delete_stream(State, StreamID, local, IsFin), EvHandlerState};
send_data(State0, StreamID, IsFin, [Data|Tail], EvHandler, EvHandlerState) ->
	State = send_data_frame(State0, StreamID, nofin, Data),
	send_data(State, StreamID, IsFin, Tail, EvHandler, EvHandlerState).

send_data_frame(State=#http2_state{socket=Socket, transport=Transport},
		StreamID, IsFin, {data, Data}) ->
	Transport:send(Socket, cow_http2:data(StreamID, IsFin, Data)),
	State;
%% @todo Uncomment this once sendfile is supported.
%send_data_frame(State=#http2_state{socket=Socket, transport=Transport},
%		StreamID, IsFin, {sendfile, Offset, Bytes, Path}) ->
%	Transport:send(Socket, cow_http2:data_header(StreamID, IsFin, Bytes)),
%	Transport:sendfile(Socket, Path, Offset, Bytes),
%	State;
%% The stream is terminated in cow_http2_machine:prepare_trailers.
send_data_frame(State=#http2_state{socket=Socket, transport=Transport,
		http2_machine=HTTP2Machine0}, StreamID, nofin, {trailers, Trailers}) ->
	{ok, HeaderBlock, HTTP2Machine}
		= cow_http2_machine:prepare_trailers(StreamID, HTTP2Machine0, Trailers),
	Transport:send(Socket, cow_http2:headers(StreamID, fin, HeaderBlock)),
	State#http2_state{http2_machine=HTTP2Machine}.

reset_stream(State0=#http2_state{socket=Socket, transport=Transport},
		StreamID, StreamError={stream_error, Reason, _}) ->
	Transport:send(Socket, cow_http2:rst_stream(StreamID, Reason)),
	case take_stream(State0, StreamID) of
		{#stream{ref=StreamRef, reply_to=ReplyTo}, State} ->
			ReplyTo ! {gun_error, self(), stream_ref(State, StreamRef), StreamError},
			State;
		error ->
			State0
	end.

connect(State=#http2_state{socket=Socket, transport=Transport, opts=Opts,
		http2_machine=HTTP2Machine0}, StreamRef, ReplyTo,
		Destination=#{host := Host0}, TunnelInfo, Headers0, InitialFlow0)
		when is_reference(StreamRef) ->
	Host = case Host0 of
		Tuple when is_tuple(Tuple) -> inet:ntoa(Tuple);
		_ -> Host0
	end,
	Port = maps:get(port, Destination, 1080),
	Authority = [Host, $:, integer_to_binary(Port)],
	PseudoHeaders = #{
		method => <<"CONNECT">>,
		authority => iolist_to_binary(Authority)
	},
	Headers1 =
		lists:keydelete(<<"host">>, 1,
		lists:keydelete(<<"content-length">>, 1, Headers0)),
	HasProxyAuthorization = lists:keymember(<<"proxy-authorization">>, 1, Headers1),
	Headers = case {HasProxyAuthorization, Destination} of
		{false, #{username := UserID, password := Password}} ->
			[{<<"proxy-authorization">>, [
					<<"Basic ">>,
					base64:encode(iolist_to_binary([UserID, $:, Password]))]}
				|Headers1];
		_ ->
			Headers1
	end,
	{ok, StreamID, HTTP2Machine1} = cow_http2_machine:init_stream(<<"CONNECT">>, HTTP2Machine0),
	{ok, nofin, HeaderBlock, HTTP2Machine} = cow_http2_machine:prepare_headers(
		StreamID, HTTP2Machine1, nofin, PseudoHeaders, Headers),
	Transport:send(Socket, cow_http2:headers(StreamID, nofin, HeaderBlock)),
	InitialFlow = initial_flow(InitialFlow0, Opts),
	Stream = #stream{id=StreamID, ref=StreamRef, reply_to=ReplyTo, flow=InitialFlow,
		authority=Authority, path= <<>>, tunnel={setup, Destination, TunnelInfo}},
	create_stream(State#http2_state{http2_machine=HTTP2Machine}, Stream);
%% Tunneled request.
connect(State, [StreamRef|Tail], ReplyTo, Destination, TunnelInfo, Headers0, InitialFlow) ->
	case get_stream_by_ref(State, StreamRef) of
		%% @todo We should send an error to the user if the stream isn't ready.
		Stream=#stream{tunnel={Proto, ProtoState0, ProtoTunnelInfo}} ->
			ProtoState = Proto:connect(ProtoState0, normalize_stream_ref(Tail),
				ReplyTo, Destination, TunnelInfo, Headers0, InitialFlow),
			store_stream(State, Stream#stream{tunnel={Proto, ProtoState, ProtoTunnelInfo}});
		#stream{tunnel=undefined} ->
			ReplyTo ! {gun_error, self(), stream_ref(State, StreamRef), {badstate,
				"The stream is not a tunnel."}},
			State;
		error ->
			error_stream_not_found(State, StreamRef, ReplyTo)
	end.

cancel(State=#http2_state{socket=Socket, transport=Transport, http2_machine=HTTP2Machine0},
		StreamRef, ReplyTo, EvHandler, EvHandlerState0) ->
	case get_stream_by_ref(State, StreamRef) of
		#stream{id=StreamID} ->
			{ok, HTTP2Machine} = cow_http2_machine:reset_stream(StreamID, HTTP2Machine0),
			Transport:send(Socket, cow_http2:rst_stream(StreamID, cancel)),
			EvHandlerState = EvHandler:cancel(#{
				stream_ref => StreamRef,
				reply_to => ReplyTo,
				endpoint => local,
				reason => cancel
			}, EvHandlerState0),
			{delete_stream(State#http2_state{http2_machine=HTTP2Machine}, StreamID),
				EvHandlerState};
		error ->
			{error_stream_not_found(State, StreamRef, ReplyTo),
				EvHandlerState0}
	end.

timeout(State=#http2_state{http2_machine=HTTP2Machine0}, {cow_http2_machine, Name}, TRef) ->
	case cow_http2_machine:timeout(Name, TRef, HTTP2Machine0) of
		{ok, HTTP2Machine} ->
			{state, State#http2_state{http2_machine=HTTP2Machine}};
		{error, Error={connection_error, _, _}, _HTTP2Machine} ->
			connection_error(State, Error)
	end.

stream_info(State, StreamRef) when is_reference(StreamRef) ->
	case get_stream_by_ref(State, StreamRef) of
		#stream{reply_to=ReplyTo, tunnel={Protocol, _, TunnelInfo=#{
				origin_host := OriginHost, origin_port := OriginPort}}} ->
			{ok, #{
				ref => StreamRef,
				reply_to => ReplyTo,
				state => running,
				tunnel => #{
					transport => case TunnelInfo of
						#{tls_proxy_pid := _} -> tls;
						_ -> tcp
					end,
					protocol => Protocol:name(),
					origin_scheme => case TunnelInfo of
						#{tls_proxy_pid := _} -> <<"https">>;
						_ -> <<"http">>
					end,
					origin_host => OriginHost,
					origin_port => OriginPort
				}
			}};
		#stream{reply_to=ReplyTo} ->
			{ok, #{
				ref => StreamRef,
				reply_to => ReplyTo,
				state => running
			}};
		error ->
			{ok, undefined}
	end;
%% Tunneled streams.
stream_info(State=#http2_state{transport=Transport}, StreamRefList=[StreamRef|Tail]) ->
	case get_stream_by_ref(State, StreamRef) of
		#stream{tunnel={Protocol, ProtoState, TunnelInfo=#{host := TunnelHost, port := TunnelPort}}} ->
			%% We must return the real StreamRef as seen by the user.
			%% We therefore set it on return, with the outer layer "winning".
			%%
			%% We also add intermediaries which are prepended to the list and
			%% therefore are ultimately given from outer to inner layer just
			%% like gun:info/1 intermediaries.
			case Protocol:stream_info(ProtoState, normalize_stream_ref(Tail)) of
				{ok, undefined} ->
					{ok, undefined};
				{ok, Info} ->
					Intermediaries1 = maps:get(intermediaries, TunnelInfo, []),
					Intermediaries2 = maps:get(intermediaries, Info, []),
					{ok, Info#{
						ref => StreamRefList,
						intermediaries => [#{
							type => connect,
							host => TunnelHost,
							port => TunnelPort,
							transport => case Transport:name() of
								tcp_proxy -> tcp;
								tls_proxy -> tls;
								TransportName -> TransportName
							end,
							protocol => http2
						}|Intermediaries1 ++ Intermediaries2]
					}}
			end;
		error ->
			{ok, undefined}
	end.

down(#http2_state{stream_refs=Refs}) ->
	maps:keys(Refs).

connection_error(#http2_state{socket=Socket, transport=Transport,
		http2_machine=HTTP2Machine, streams=Streams},
		Error={connection_error, Reason, HumanReadable}) ->
	Pids = lists:usort(maps:fold(
		fun(_, #stream{reply_to=ReplyTo}, Acc) -> [ReplyTo|Acc] end,
		[], Streams)),
	_ = [Pid ! {gun_error, self(), {Reason, HumanReadable}} || Pid <- Pids],
	Transport:send(Socket, cow_http2:goaway(
		cow_http2_machine:get_last_streamid(HTTP2Machine),
		Reason, <<>>)),
	{error, Error}.

%% Stream functions.

error_stream_closed(State, StreamRef, ReplyTo) ->
	ReplyTo ! {gun_error, self(), stream_ref(State, StreamRef), {badstate,
		"The stream has already been closed."}},
	State.

error_stream_not_found(State, StreamRef, ReplyTo) ->
	ReplyTo ! {gun_error, self(), stream_ref(State, StreamRef), {badstate,
		"The stream cannot be found."}},
	State.

%% Streams.

stream_ref(#http2_state{base_stream_ref=undefined}, StreamRef) ->
	StreamRef;
stream_ref(#http2_state{base_stream_ref=BaseStreamRef}, StreamRef)
		when is_reference(BaseStreamRef) ->
	[BaseStreamRef, StreamRef];
stream_ref(#http2_state{base_stream_ref=BaseStreamRef}, StreamRef) ->
	BaseStreamRef ++ [StreamRef].

get_stream_by_id(#http2_state{streams=Streams}, StreamID) ->
	maps:get(StreamID, Streams).

get_stream_by_ref(#http2_state{streams=Streams, stream_refs=Refs}, StreamRef) ->
	case maps:get(StreamRef, Refs, error) of
		error -> error;
		StreamID -> maps:get(StreamID, Streams)
	end.

create_stream(State=#http2_state{streams=Streams, stream_refs=Refs},
		Stream=#stream{id=StreamID, ref=StreamRef}) ->
	State#http2_state{
		streams=Streams#{StreamID => Stream},
		stream_refs=Refs#{StreamRef => StreamID}
	}.

store_stream(State=#http2_state{streams=Streams}, Stream=#stream{id=StreamID}) ->
	State#http2_state{streams=Streams#{StreamID => Stream}}.

take_stream(State=#http2_state{streams=Streams0, stream_refs=Refs}, StreamID) ->
	case maps:take(StreamID, Streams0) of
		{Stream=#stream{ref=StreamRef}, Streams} ->
			{Stream, State#http2_state{
				streams=Streams,
				stream_refs=maps:remove(StreamRef, Refs)
			}};
		error ->
			error
	end.

maybe_delete_stream(State=#http2_state{http2_machine=HTTP2Machine}, StreamID, local, fin) ->
	case cow_http2_machine:get_stream_remote_state(StreamID, HTTP2Machine) of
		{ok, fin} -> delete_stream(State, StreamID);
		{error, closed} -> delete_stream(State, StreamID);
		_ -> State
	end;
maybe_delete_stream(State=#http2_state{http2_machine=HTTP2Machine}, StreamID, remote, fin) ->
	case cow_http2_machine:get_stream_local_state(StreamID, HTTP2Machine) of
		{ok, fin, _} -> delete_stream(State, StreamID);
		{error, closed} -> delete_stream(State, StreamID);
		_ -> State
	end;
maybe_delete_stream(State, _, _, _) ->
	State.

delete_stream(State=#http2_state{streams=Streams, stream_refs=Refs}, StreamID) ->
	#{StreamID := #stream{ref=StreamRef}} = Streams,
	State#http2_state{
		streams=maps:remove(StreamID, Streams),
		stream_refs=maps:remove(StreamRef, Refs)
	}.